Many players don't give themselves a chance to make good "golf swings" because they swing the club with just their hands and arms. First, they pick the club up on the takeaway, which results in little or no shoulder turn during their backswing. This almost always prevents them from shifting their weight to their back foot, which causes a reverse pivot and eliminates power during the swing. An important fact to remember is: if you have a poor move away from the ball on your backswing you most likely will have a poor move through the ball on your forwardswing; resulting in a poor golf shot.
The simple way to improve your backswing and follow through is as follows:
Start your backswing by turning your left shoulder away from the target, (if you are a right-handed golfer), and just let your hands and arms naturally go to the top of your backswing. You should notice a wider and fuller backswing, without additional effort on your part. You should also feel your weight easily transfer to your right side. You are now in the correct position to unleash a powerful swing through the hitting area.
Start the downswing by simply turning your left shoulder back toward the target and allowing your right shoulder to keep moving "down the target line" until you complete the follow through. Don't hold your weight back! All your weight should be on your front foot, (left foot for right-handed golfers), at the finish.
As you practice using your shoulders also "feel" your weight move with the club. When you take the club back, allow your weight go back with it. Now as you swing the club through let your weight go forward. You should "feel" a longer, wider and much more powerful swing.